The power grid reactive power compensation device including a shunt capacitor bank is widely used in the power system. The connected compensation device changes the harmonic impedance properties of the power grid, and may cause resonance phenomena in case that no measure or an inappropriate measure is taken, such that the compensation device and adjacent electric devices in the connected power grid may be seriously damaged or destroyed.
In the prior methods for analyzing the resonance damages caused by running capacitors, with the system impedance and the background harmonic voltage at the connection point(s) to the capacitor(s) known, an offline prediction is performed as whether a connection of the capacitor into the power grid under the background harmonic may cause a resonance phenomenon, and whether the running capacitor is beyond its limit range. Herein as shown in FIG. 1, the power source open circuit voltage
      E    =                  E        1            +                        ∑          n                ⁢                  E          n                      ,wherein E1 is the fundamental voltage,
      ∑    n    ⁢      E    n  is the background harmonic; Zsys is the system impedance and Zsys=Rsys+jXsys; C is the capacitor to be connected in.
By the above analysis to the damages of the resonance phenomena, the following problems may be presented: with the harmonic changing from time to time, the prior offline early-warning manner cannot precisely predict whether a connection of the capacitor into the power grid may cause a resonance phenomenon; in addition, with only the influence of a single capacitor on the resonance phenomenon is under consideration, the result of the above prediction is not sufficiently complete. However, in the prior art, there is not any solution for online analyzing the damages by resonance phenomenon in consideration of connection of capacitors, in a form of capacitor bank, into the power grid.